<!DOCTYPE html>
<html lang="zh">
<head>
    <meta charset="UTF-8">
    <title>js===测试</title>
</head>
<body>
<script type="text/javascript">
    //字符串相等比较用 ===而不是==
    var k='';
    //都是true
    alert(k==='')
    alert(k==="")
</script>
</body>
</html>